// Copyright 2015-2017 Benjamin Fry <benjaminfry@me.com>
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// https://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// https://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

//! System configuration loading
//!
//! This module is responsible for parsing and returning the configuration from
//!  the host system. It will read from the default location on each operating
//!  system, e.g. most Unixes have this written to `/etc/resolv.conf`

use std::fs;
use std::io;
use std::path::Path;
use std::str::FromStr;
use std::time::Duration;

use crate::config::{NameServerConfig, ResolverConfig, ResolverOpts};
use crate::proto::NetError;
use crate::proto::rr::Name;

pub fn read_system_conf() -> Result<(ResolverConfig, ResolverOpts), NetError> {
    read_resolv_conf("/etc/resolv.conf")
}

fn read_resolv_conf<P: AsRef<Path>>(path: P) -> Result<(ResolverConfig, ResolverOpts), NetError> {
    parse_resolv_conf(fs::read(path)?)
}

pub fn parse_resolv_conf<T: AsRef<[u8]>>(
    data: T,
) -> Result<(ResolverConfig, ResolverOpts), NetError> {
    let parsed_conf = resolv_conf::Config::parse(&data)
        .map_err(|e| io::Error::other(format!("Error parsing resolv.conf: {e}")))?;
    into_resolver_config(parsed_conf)
}

// TODO: use a custom parsing error type maybe?
fn into_resolver_config(
    parsed_config: resolv_conf::Config,
) -> Result<(ResolverConfig, ResolverOpts), NetError> {
    let domain = if let Some(domain) = parsed_config.get_system_domain() {
        // The system domain name maybe appear to be valid to the resolv_conf
        // crate but actually be invalid. For example, if the hostname is "matt.schulte's computer"
        // In order to prevent a hostname which macOS or Windows would consider
        // valid from returning an error here we turn parse errors to options
        Name::from_str(domain.as_str()).ok()
    } else {
        None
    };

    // nameservers
    let nameservers = parsed_config
        .nameservers
        .iter()
        .map(|ip| NameServerConfig::udp_and_tcp(ip.into()))
        .collect::<Vec<_>>();
    if nameservers.is_empty() {
        Err(io::Error::other("no nameservers found in config"))?;
    }

    // search
    let mut search = vec![];
    for search_domain in parsed_config.get_last_search_or_domain() {
        // Ignore invalid search domains
        if search_domain == "--" {
            continue;
        }

        search.push(
            Name::from_str_relaxed(search_domain)
                .map_err(|e| io::Error::other(format!("Error parsing resolv.conf: {e}")))?,
        );
    }

    let config = ResolverConfig::from_parts(domain, search, nameservers);

    let options = ResolverOpts {
        ndots: parsed_config.ndots as usize,
        timeout: Duration::from_secs(u64::from(parsed_config.timeout)),
        attempts: parsed_config.attempts as usize,
        edns0: parsed_config.edns0,
        ..ResolverOpts::default()
    };

    Ok((config, options))
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::proto::rr::Name;
    use std::env;
    use std::net::*;
    use std::str::FromStr;

    fn empty_config(name_servers: NameServerConfig) -> ResolverConfig {
        ResolverConfig::from_parts(None, vec![], vec![name_servers])
    }

    fn nameserver_config(ip: &str) -> NameServerConfig {
        let mut server = NameServerConfig::udp_and_tcp(IpAddr::from_str(ip).unwrap());
        server.trust_negative_responses = false;
        server
    }

    fn tests_dir() -> String {
        let server_path = env::var("TDNS_WORKSPACE_ROOT").unwrap_or_else(|_| "../..".to_owned());
        format!("{server_path}/crates/resolver/tests")
    }

    #[test]
    fn test_name_server() {
        let parsed = parse_resolv_conf("nameserver 127.0.0.1").expect("failed");
        let cfg = empty_config(nameserver_config("127.0.0.1"));
        assert_eq!(cfg.name_servers()[0].ip, parsed.0.name_servers()[0].ip);
        is_default_opts(parsed.1);
    }

    #[test]
    fn test_search() {
        let parsed = parse_resolv_conf("search localnet.\nnameserver 127.0.0.1").expect("failed");
        let mut cfg = empty_config(nameserver_config("127.0.0.1"));
        cfg.add_search(Name::from_str("localnet.").unwrap());
        assert_eq!(cfg.search(), parsed.0.search());
        is_default_opts(parsed.1);
    }

    #[test]
    fn test_skips_invalid_search() {
        let parsed =
            parse_resolv_conf("\n\nnameserver 127.0.0.53\noptions edns0 trust-ad\nsearch -- lan\n")
                .expect("failed");
        let mut cfg = empty_config(nameserver_config("127.0.0.53"));

        {
            assert_eq!(cfg.name_servers()[0].ip, parsed.0.name_servers()[0].ip);
            is_default_opts(parsed.1);
        }

        // This is the important part, that the invalid `--` is skipped during parsing
        {
            cfg.add_search(Name::from_str("lan").unwrap());
            assert_eq!(cfg.search(), parsed.0.search());
        }
    }

    #[test]
    fn test_underscore_in_search() {
        let parsed =
            parse_resolv_conf("search Speedport_000\nnameserver 127.0.0.1").expect("failed");
        let mut cfg = empty_config(nameserver_config("127.0.0.1"));
        cfg.add_search(Name::from_str_relaxed("Speedport_000").unwrap());
        assert_eq!(cfg.search(), parsed.0.search());
        is_default_opts(parsed.1);
    }

    #[test]
    fn test_domain() {
        let parsed = parse_resolv_conf("domain example.com\nnameserver 127.0.0.1").expect("failed");
        let mut cfg = empty_config(nameserver_config("127.0.0.1"));
        cfg.set_domain(Name::from_str("example.com").unwrap());
        assert_eq!(cfg.name_servers()[0].ip, parsed.0.name_servers()[0].ip);
        assert_eq!(cfg.domain(), parsed.0.domain());
        is_default_opts(parsed.1);
    }

    #[test]
    fn test_read_resolv_conf() {
        read_resolv_conf(format!("{}/resolv.conf-simple", tests_dir())).expect("simple failed");
        read_resolv_conf(format!("{}/resolv.conf-macos", tests_dir())).expect("macos failed");
        read_resolv_conf(format!("{}/resolv.conf-linux", tests_dir())).expect("linux failed");
    }

    /// Validate that all options set in `into_resolver_config()` are at default values
    fn is_default_opts(opts: ResolverOpts) {
        assert_eq!(opts.ndots, 1);
        assert_eq!(opts.timeout, Duration::from_secs(5));
        assert_eq!(opts.attempts, 2);
    }
}
